The amount of wireless data is growing at unprecedented pace in the last few years, pushing the capacity of current macro cellular deployments. Cellular communications systems, which utilize microwave spectrum bands (300 MHz to 3 GHz), are becoming capacity limited due to interference and traffic load. The use of high frequency bands, where vast amounts of bandwidth is available, is considered to be a crucial technology for future generation communication systems. The use of these frequency bands (e.g., 28, 38, 60 and 73 GHz) can mitigate the problem of capacity currently observed.
Propagation in the millimeter band (mmWave) is much more challenging than in the microwave band, resulting in a more stringent link budget at mmWave band than at microwave band. Transmitters and receivers equipped with a larger number of antenna arrays are a viable solution to compensate for the mmWave extra path loss by beamforming.
Because antenna size is inversely proportional to the carrier frequency, the use of these high frequency bands reduces the antenna size considerably. As such, a larger number of transmit and receive antenna arrays at both network and terminal sides may be employed.
Hybrid antenna architecture is likely to be used to trade off hardware complexity, power consumption, and the performance and coverage of the system. Hybrid antenna architecture typically includes analog (phase shifter) and digital (baseband pre-coder) beamforming parts.